#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<sys/types.h>
#include<sys/wait.h>
#include<unistd.h>
#include<string>
#include<fcntl.h>


#define MAX_ENVS 100
char* g_env[MAX_ENVS];
int g_envs = 0;


#define COMMAND_SIZE 1024
#define FORMAT "[%s@%s %s]# "

#define MAXARGC 128
char* g_argv[MAXARGC];
int g_argc = 0;

int lastcode = 0;

char cwd[1024];
char cwdenv[1024];

#define NONE_REDIR 0
#define INPUT_REDIR 1
#define OUTPUT_REDIR 2
#define APPEND_REDIR 3

int redir = NONE_REDIR;
std::string filename;



const char* GetUserName(){
    const char* name = getenv("USER");
    return name == NULL ? "None":name;
}

const char* GetHostName(){
    const char* name = getenv("HOSTNAME");
    return name == NULL ? "None":name;
}

const char* GetPwd(){
    //const char* pwd = getenv("PWD");
    const char* pwd = getcwd(cwd,sizeof(cwd));
    if(pwd != NULL){
        snprintf(cwdenv,sizeof(cwdenv),"PWD=%s",cwd);
        putenv(cwdenv);
    }
    return pwd == NULL ? "None":pwd;
}

const char* GetHome(){
    const char* home = getenv("HOME");
    return home == NULL ? "":home;
}

void InitEnv(){
    extern char** environ;

    memset(g_env,0,sizeof(g_env));
    g_envs = 0;

    for(int i = 0;environ[i];i++){
        g_env[i] = (char*)malloc(strlen(environ[i])+1);
        g_env[g_envs] = environ[i];
        g_envs++;
    }

    g_env[g_envs++] = (char*)"HAHA=for_test";
    g_env[g_envs] = NULL;
    for(int i = 0;g_env[i];i++){
        putenv(g_env[i]);
    }
    environ = g_env;
}


std::string DirName(const char* pwd){
#define SLASH "/"
    std::string dir = pwd;
    if(dir == SLASH) return SLASH;
    auto pos = dir.rfind(SLASH); 
    if(pos == std::string::npos) return "BUG?";
    return dir.substr(pos + 1);
}

void MakeCommandLine(char cmd_prompt[],int size){
    snprintf(cmd_prompt,size,FORMAT,GetUserName(),GetHostName(),DirName(GetPwd()).c_str());
}

void PrintCommandLine(){
    char prompt[COMMAND_SIZE];
    MakeCommandLine(prompt,sizeof(prompt));
    printf("%s",prompt);
}

bool GetCommandLine(char out[],int size){
    char* c = fgets(out,size,stdin);
    if(c == NULL) return false;
    out[strlen(out) - 1] = 0; 
    if(strlen(out) == 0) return false;
    return true;
}

bool CommandPrase(char command[]){
#define SEP " "
    g_argc = 0;
    g_argv[g_argc++] = strtok(command,SEP);
    while((bool)(g_argv[g_argc++] = strtok(nullptr,SEP)));
    g_argc--;
    return true;
}

bool cd(){
    if(g_argc == 1){
        std::string home = GetHome();
        if(home.empty()){
            return false;
        }
        chdir(home.c_str());
    }
    else{
        std::string where = g_argv[1];
        chdir(where.c_str());
    }
    return true;
}

bool echo(){
    std::string opt = g_argv[1];
    if(opt == "$?"){
        std::cout<<lastcode<<std::endl;
        lastcode = 0;
    }
    else if(opt[0] == '$'){
        std::string env_name = opt.substr(1);
        const char* env_val = getenv(env_name.c_str());
        if(env_val != NULL){
            std::cout<<env_val<<std::endl;
        }
    }
    else{
        std::cout<<opt<<std::endl;
    }
    return true;
}

void TrimSpace(char* cmd,int& end){
    if(isspace(cmd[end]))
        end++;
}

void RedirCheck(char* command){
    filename.clear();
    redir = NONE_REDIR;

    int begin = 0;
    int end = strlen(command) - 1;

    while(end > begin){
        if(command[end] == '<'){
            command[end++] = 0;
            TrimSpace(command,end);
            redir = INPUT_REDIR;
            filename = command + end;
            break;
        }
        else if(command[end] == '>'){
            if(command[end - 1] == '>'){
                command[end - 1] = 0;
                redir = APPEND_REDIR;
            }
            else{
                redir = OUTPUT_REDIR;
            }
            command[end++] = 0;
            TrimSpace(command,end);
            filename = command + end;
            break;
        }
        else 
            end--;
    }

}


bool CheckAndBuildIn(){
    std::string cmd = g_argv[0];
    if(cmd == "cd"){
        cd();
        return true;
    }
    else if(cmd == "echo"){
        echo();
        return true;
    }
    return false;
}


int Execute(){

    pid_t id = fork();
    if(id == 0){
        int fd = -1;
        if(redir == INPUT_REDIR){
            fd = open(filename.c_str(),O_RDONLY);
            if(fd < 0){
                exit(1);
            }
            dup2(fd,0);
            close(fd);
        }
        else if(redir == OUTPUT_REDIR){
            fd = open(filename.c_str(),O_CREAT|O_WRONLY|O_TRUNC,0666);
            if(fd < 0)
                exit(2);
            dup2(fd,1);
            close(fd);
        }
        else if(redir == APPEND_REDIR){
            fd = open(filename.c_str(),O_CREAT|O_WRONLY|O_APPEND,0666);
            if(fd < 0)
                exit(3);
            dup2(fd,1);
            close(fd);
        }


        execvp(g_argv[0],g_argv);
        exit(4);
    }
    int status = 0;
    pid_t rid = waitpid(id,&status,0);
    if(rid > 0){
        lastcode = WEXITSTATUS(status);
    }
    return 0;
}


int main(){
    while(1){
        PrintCommandLine();
        char commandline[COMMAND_SIZE];
        if(!GetCommandLine(commandline,sizeof(commandline)))
            continue;
        RedirCheck(commandline);
        CommandPrase(commandline);
        if(CheckAndBuildIn())
            continue;
        Execute();
    }
    return 0;
}
